Tuning a Dual-Band Bow-tie Slot

Antenna with Parabolic Radiating

Slots for the 900 MHz and 2400

MHz Bands

Layne A. Berge

Michael T. Reich

Masud A. Aziz

Benjamin D. Braaten Department of Electrical and

Computer Engineering

North Dakota State University

Fargo, ND, USA

• Introduction and background information

• Purpose of research

• Simulated and measured results

• Discussion

• Conclusion

Overview

Introduction

M. Miao, B. Ooi, and P. Kooi, “Broadband CPW-fed wide slot antenna,”Microwave and Optical Technology Letters, vol. 25, no. 3, pp. 206–211,2000.

•Planar, bow-tie, CPW

fed, slot antenna

•Original design

maintained broadband

operation between 3

and 5 GHz

Background

•Planar antennas are simple to fabricate in-house

•CPW (coplanar waveguide) feed allows balanced

excitation

•Bow-tie antenna design has a dipole like gain

pattern

Purpose of Research

•Create an antenna design using a lower

permittivity substrate (original ɛr = 10.1)

•Dual-band operation at lower, consumer-band

frequencies

•900 MHz

•2400 MHz

Design

H = 140 mm

W = 240 mm,

Bw = 100.2 mm

Bi = 8 mm

Bo = 70.3 mm

g= 0.4 mm

d = 4.6 mm

S = 7.5 mm

Design

•Rogers 4003C

•Ɛr = 3.55

•Thickness =

1.6 mm

Design

•Parabolic curves emulate a

Vivaldi antenna design

•Broadband

•Greater slot perimeter =

longer path taken by currents

J. Mandeep and M. Nicholas, “Design An

X-Band Vivaldi Antenna,” Microwaves &

RF, vol. 47, no. 8, 2008.

Measurement and Simulation Results

•Compared both Method of

Moments and Finite-

Element Method

•Good correlation between

simulated and measured

results

•Dual-band operation at 900

MHz and 2400 MHz

Measurement and Simulation Results

•Gain at 900 MHz in the y-z plane (left) and x-z plane (right)

•Gain pattern similar to a dipole antenna

•Simulated gain excursion caused by ideal assumptions (infinite

substrate layer)

Measurement and Simulation Results

•Gain at 2400 MHz in the y-z plane (left) and x-z plane (right)

•Gain pattern deviates from that of a dipole at high frequencies

•Caused by too large of a slot (electrically large dipole antenna →

favors side-lobes)

Measurement and Simulation Results

•Surface currents at 900 MHz (left) and 2400 MHz (right)

•Too large of slot evident in “odd” surface currents in 2400 MHz plot

(right)

Measurement and Simulation Results

•Field strength at 900 MHz in the y-z plane (left) and x-z plane

(right)

•Low cross-polarization in both plots

•Correlates well with gain plots

Measurement and Simulation Results

•Field strength at 2400 MHz in the y-z plane (left) and x-z plane

(right)

•Non-negligible cross-polarization evident in each plot

•Reinforces distorted gain patterns

Discussion • Deviation from simulated and measured gain

results at 900 MHz occurred because of ideal

assumption by software (infinite substrate)

• Poor gain plots at 2400 MHz

– Asymmetries partly caused by radiation losses through

the substrate

– Main cause was found to be the slot width being near

1.5λ

– Large slot results in prominent side lobes

– Similar to results for electrically long dipole antennas

Discussion • Maintained large bandwidth at both operating

frequencies (Return Loss > 10 dB)

– 602 MHz bandwidth at 900 MHz

– 229 MHz bandwidth at 2400 MHz

• Used a lower permittivity substrate

– Less loss

• Curved slot sides presented a longer path to

currents than a comparable straight side

Conclusion • Created a dual-band bow-tie slot antenna

operating at 900 MHz and 2400 MHz

• Used a lower permittivity substrate than

previous designs

• Used curved slot sides in order to reduce size

of antenna

• Gain pattern at 2400 MHz was distorted

– Slot width too wide

Questions?

Thank you for listening!